1. Field
Embodiments of the present invention relate to a structure of blades of a propeller fan used for an air conditioner.
2. Description of the Related Art
As shown in FIG. 1, when a typical blade 110A formed in a smoothly curved shape over the entire body thereof without a projection or a recessed portion thereon rotates, the air stream near the blade pressure surface 104A is inclined toward the outer edge of the blade at the blade outlet (the blade trailing edge 103A) by centrifugal force. Due to the incline stream, the stream near the cylindrical hub 111A at the center of the fan is likely to become unstable, degrading the pressure efficiency.
To address this situation, an attempt has been made to create uniform distribution of the stream in a radial direction by forming a swollen portion 106B near the blade trailing edge 103B of the propeller fan 100B such that the swollen portion 106B is swollen in an arc shape and thus convex toward the suction surface 105B and facilitating outflow from the swollen portion 106B, as shown in FIG. 2.
However, in the case that a portion of the blade trailing edge 103B is formed to be swollen, the cross section of this portion of the blade taken at the same radial distance from the center forms a line smoothly curved over the chord of the blade in the rotational direction. Accordingly, a recognizable portion of the stream that is not propelled by the blade may be produced at the trailing edge 103B of the blade, resulting in lower air blowing. In addition, since the trailing edge 103B of the blade has an arc-shaped swollen portion 106B and the air smoothly flows to this portion in a perpendicular approximately perpendicular to the arc, the force to attract the outwardly inclined airstream inward is weak. Therefore, the conventional propeller fan may not greatly increase the pressure efficiency.